Summary

This simple mount allowed me to put my Telstra TV 1 below my Kogan TV mount. The arm piece is likely not ideal for many but worked well enough that I didn’t need to keep iterating just a little holder with Double sided tape to stop any movement. The Hanger chassis is relatively ubiquitous with 3 M3 Heatset slots in the back and step files attached so that you could modify for your own purposes. Files should import in the correct orientation to print. Design was done with Onshape as a simple Sketch Extrude process, all edges chamfered with minor iterations to make more friendly for printing. No supports, brim or anything special required.

Holder uses 60.1g of filament with my settings
Arm uses 28.6g of filament with my settings.
I printed this due to inattention at 4x4x4 at 20% infill which seems to be overkill for the task at hand but I’m not reprinting for overkill.
PLA is fine for this purpose and with the updated revision there is now enough open air surrounding to stop the small amount of wasted heat energy from melting or softening the plastic.
Only hardware needed for most of the Kogan TV rails is the
3 x M3 x 16 & 3 x M3 Heatset inserts to attach the arm to the Hanger.
In my case 2 small pieces of double-sided tape were needed to stabilise the print as well so that it wasn’t on an angle.

Please feel free to remix as needed or comment for any changes you might want to see.
Updates
V1_1 on arm – Updated orientation so that it is in correct orientation to print upon import.
V1_1 on holder Adjusted original Dimensions to allow for more clearance.
V1_2 on holder Opened up one side to allow for more cooling and slightly increased clearance with reinforcements done to the back Arm Mount and basic refinements done including chamfers and minor clean-up of base geometry.
V1_3 Updated Orientation so that It is in correct orientation to print upon import.

Post-Printing

            Sink in M3 Heatset Inserts
                
            Bolt arm to M3 Heatset inserts, this was sized for M3 x 16mm Bolts.

How I Designed This

                Design Process
            Went through the process of designing the base with a sketch and 2mm extrude ensuring that extra construction lines were in place for walls.

Extruded base, then walls.

Made an offset plane and used that for the first sketch as an extrude for the top.

Sketched the back with a hole through to allow for cables. Remove tool used for hole.

Sketched sides and removed as part of revisions. Progressed mounting concept with a sketch / extrude along the back of the model to allow for M3 Heatset inserts.

M3 Heatset inserts are based on some research notes with hole tool going at 5.1/5.31/3.8

These are a looser fit for my normal heatsets then I like but helps to keep it pretty easy to get ones to fit. M3 Bolt holes done using standard tools in hole tool.

Arm made simply by making a new parts studio and copying base model, copied over base model mount to new sketch and extruded from there. Chamfers used to avoid right angle stress points and to refine design.